There has been a lot of commotion and even a book with having Ruby on Rails run on the Java VM. But looking past the JRuby hype it is clear that PHP has a several orders of magnitude more open source code, projects, and corporate backing than Ruby on Rails. The folks behind the Resin application server have the ubiquitous of PHP and have developed Quercus, a PHP 5 implementation written in Java.

Quercus is available with the latest Resin but it is also available for download as a WAR file which can be deployed on Resin or other application Servers such as GlassFish.